c, x + $\frac{3}{7}$ = $\frac{1}{4}$ + $\frac{1}{5}$
x + $\frac{3}{7}$ = $\frac{9}{20}$
x = $\frac{9}{20}$ - $\frac{3}{7}$
x = $\frac{3}{140}$
e, ║x + $\frac{1}{3}$║ = 2
⇒ x + $\frac{1}{3}$ = 2 hoặc x + $\frac{1}{3}$ = - 2
x = 2 - $\frac{1}{3}$ x = -2 - $\frac{1}{3}$
x = $\frac{5}{3}$ x = - $\frac{7}{3}$
f, ║ $\frac{5}{3}$ - x ║ + 1 = 7
║ $\frac{5}{3}$ - x ║ = 6
⇒ $\frac{5}{3}$ - x = 6 hoặc $\frac{5}{3}$ - x = -6
x = $\frac{5}{3}$ - 6 x = $\frac{5}{3}$ - ( - 6)
x = - $\frac{13}{3}$ x = $\frac{23}{3}$
